Multi-layered unit including electrode and dielectric layer

ABSTRACT

A multi-layered unit according to the present invention includes a support substrate formed of platinum (Pt), a buffer layer formed on the support substrate and formed of a dielectric material containing a bismuth layer structured compound having an excellent orientation characteristic and a composition represented by Bi 4 Ti 3 O 12  and oriented in the c axis direction, and a dielectric layer formed on the buffer layer, formed of a dielectric material containing a bismuth layer structured compound having an excellent characteristic as a capacitor material and a composition represented by SrBi 4 T 4 O 15  and containing the bismuth layer structured compound oriented in the c axis direction. Since the thus constituted multi-layered unit includes the dielectric layer containing the bismuth layer structured compound oriented in the c axis direction, in the case of, for example, providing an upper electrode on the dielectric layer to form a thin film capacitor and applying a voltage between the support substrate serving as an electrode layer and the upper electrode, the direction of the electric field substantially coincides with the c axis of the bismuth layer structured compound contained in the dielectric layer. As a result, since the ferroelectric property of the bismuth layer structured compound contained in the dielectric layer can be suppressed and the paraelectric property thereof can be fully exhibited, it is possible to fabricate a thin film capacitor having a small size, large capacitance and an excellent dielectric characteristic.

BACKGROUND OF THE INVENTION

The present invention relates to a multi-layered unit including anelectrode and a dielectric layer and, particularly, to a multi-layeredunit suitable for fabricating a thin film capacitor having a small sizeand large capacitance and suitable for fabricating an inorganic EL(electro-luminescence) device capable of emitting light having highluminescence.

DESCRIPTION OF THE PRIOR ART

Recently, the operating frequency of LSIs (Large Scale Integratedcircuits), typically CPUs (Central Processing Units), has become higherand higher. In the LSI having a high operating frequency, power supplynoise is very likely to be generated, and once power supply noiseoccurs, a voltage drop occurs due to parasitic resistance and parasiticinductance of the power supply wiring, causing the LSI to operateerroneously.

In order to prevent such a voltage drop caused by power supply noise, adecoupling capacitor is generally connected between the terminals of theLSI power supply. In the case where a decoupling capacitor is connectedbetween the terminals of the LSI power supply, the impedance of thepower supply wiring decreases to effectively prevent voltage drop causedby power supply noise.

The impedance required of the power supply wiring is proportional to theoperating voltage of the LSI and inversely proportional to theintegration density of the LSI, the switching current of the LSI and theoperating frequency of the LSI. Therefore, in current LSIs, which havehigh integration density, low operating voltage and high operatingfrequency, the impedance required of the power supply wiring isextremely low.

In order to achieve such low impedance of the power supply wiring, it isnecessary to increase the capacitance of the decoupling capacitor andconsiderably lower the inductance of the wiring connecting the terminalsof the LSI power supply and the decoupling capacitor.

As a decoupling capacitor having a large capacitance, an electrolyticcapacitor or a multilayer ceramic capacitor is generally employed.However, since the size of an electrolytic capacitor or multilayerceramic capacitor is relatively large, it is difficult to integrate itwith an LSI. Therefore, the electrolytic capacitor or multilayer ceramiccapacitor has to be mounted on a circuit substrate independently of theLSI and, as a result, the length of wiring for connecting the terminalsof the LSI power supply and the decoupling capacitor is inevitably long.Accordingly, in the case where an electrolytic capacitor or a multilayerceramic capacitor is employed as a decoupling capacitor, it is difficultto lower the inductance of the wiring for connecting the terminals ofthe LSI power supply and the decoupling capacitor.

In order to shorten the wiring for connecting the terminals of the LSIpower supply and the decoupling capacitor, use of a thin film capacitorhaving a smaller size than that of an electrolytic capacitor or amultilayer ceramic capacitor is suitable.

Japanese Patent Application Laid Open No. 2001-15382 discloses a thinfilm capacitor having a small size and large capacitance which employsPZT, PLZT, (Ba, Sr) TiO₃ (BST), Ta₂O₅ or the like as a dielectricmaterial.

However, the thin film capacitor employing any one of the abovementioned materials is disadvantageous in that the temperaturecharacteristic thereof is poor. For example, since the dielectricconstant of BST has a temperature dependency of −1000 to −4000 ppm/° C.,in the case where BST is employed as a dielectric material, thecapacitance of the thin film capacitor at 80° C. varies between −6% and−24% in comparison with that at 20° C. Therefore, a thin film capacitoremploying BST as a dielectric material is not suitable for use as adecoupling capacitor for a high operating frequency LSI whose ambienttemperature frequently reaches 80° C. or higher owing to heat generatedby electric power consumption.

Furthermore, the dielectric constant of a dielectric thin film formed ofany one of the above mentioned materials decreases as the thicknessthereof decreases and the capacitance thereof greatly decreases when anelectric field of 100 kV/cm, for example, is applied thereto. Therefore,in the case where any one of the above mentioned materials is used as adielectric material for a thin film capacitor, it is difficult tosimultaneously make the thin film capacitor small and the capacitancethereof great.

In addition, Moreover, since the surface roughness of a dielectric thinfilm formed of any one of the above mentioned materials is high, itsinsulation performance tends to be lowered when formed thin.

It might be thought possible to overcome these problems by using abismuth layer structured compound as a dielectric material for a thinfilm capacitor. The bismuth layer structured compound is discussed byTadashi Takenaka in “Study on the particle orientation of bismuth layerstructured ferroelectric ceramics and their application to piezoelectricor pyroelectric materials” Engineering Doctoral Thesis at the Universityof Kyoto (1984), Chapter 3, pages 23 to 36.

It is known that the bismuth layer structured compound has ananisotropic crystal structure and behaves as a ferroelectric materialbut that the bismuth layer structured compound exhibits only weakproperty as a ferroelectric material and behaves like as a paraelectricmaterial along a certain axis of orientation.

The property of the bismuth layer structured compound as a ferroelectricmaterial is undesirable when the bismuth layer structured compound isutilized as a dielectric material for a thin film capacitor since itcauses variation in dielectric constant. Therefore, when a bismuth layerstructured compound is used as a dielectric material for a thin filmcapacitor, it is preferable that its paraelectric property can be fullyexhibited.

Therefore, a need has been felt for the development of a thin filmcapacitor of small size, large capacitance and excellent dielectriccharacteristic that has a dielectric layer in which a bismuth layerstructured compound oriented in the axis of orientation along which thebismuth layer structured compound exhibits only weak property as aferroelectric material and behaves like a paraelectric material.

On the other hand, it is necessary in order to fabricate an inorganic EL(electro-luminescence) device for emitting light having highluminescence to provide a dielectric layer having a high insulatingproperty between an electrode and an inorganic EL device and it istherefore required to develop an inorganic EL device provided with adielectric layer in which a bismuth layer structured compound orientedin the axis of orientation along which the bismuth layer structuredcompound exhibits only weak property as a ferroelectric material andbehaves like a paraelectric material.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide amulti-layered unit suitable for fabricating a thin film capacitor havinga small size, large capacitance and an excellent dielectriccharacteristic and suitable for fabricating an inorganic EL(electro-luminescence) device capable of emitting light having highluminescence.

The above and other objects of the present invention can be accomplishedby a multi-layered unit including a support substrate formed of aconductive material, a buffer layer formed on the support substrate of abismuth layer structured compound oriented in the [001] direction, and adielectric layer formed on the buffer layer of a dielectric materialcontaining a bismuth layer structured compound oriented in the [001]direction, a bismuth layer structured compound having an excellentorientation characteristic being selected as the bismuth layerstructured compound contained in the buffer layer and a bismuth layerstructured compound having an excellent characteristic as a capacitormaterial being selected as the bismuth layer structured compoundcontained in the dielectric layer, thereby forming an interface betweenthe buffer layer and the dielectric layer.

In the present invention, the [001] direction as termed herein means the[001] direction of a cubic crystal, a tetragonal crystal, a monocliniccrystal or an orthorhombic crystal.

According to the present invention, since the support substrate of themulti-layered unit is formed of a conductive material, the supportsubstrate can serve as an electrode and it is therefore possible to makea thin film capacitor or an inorganic EL device fabricated using themulti-layered unit according to the present invention much thinner.

Further, according to the present invention, since the support substrateof the multi-layered unit is formed of a conductive material, thesupport substrate can serve as an electrode and it is therefore possibleembed a thin film capacitor fabricated using the multi-layered unitaccording to the present invention in a printed circuit substrate madeof resin, thereby fabricating a printed circuit substrate including athin film capacitor. In this case, since it is unnecessary to usesilicon, it is possible to fabricate the printed circuit substrateincluding the thin film capacitor at low cost.

Furthermore, according to the present invention, since the multi-layeredunit is formed with the buffer layer containing a bismuth layerstructured compound having an excellent orientation characteristic andoriented in the [001] direction, the dielectric layer of a dielectricmaterial containing a bismuth layer structured compound oriented in the[001] direction can be desirably formed on the buffer layer byepitaxially growing the dielectric material containing the bismuth layerstructured compound having an excellent characteristic as a capacitormaterial.

Therefore, according to the present invention, since the c axis of thebismuth layer structured compound having an excellent characteristic asa capacitor material and contained in a dielectric layer can be orientedso as to be perpendicular to the electrode layer, in the case of, forexample, providing an upper electrode on the dielectric layer andapplying a voltage between the electrode layer and the upper electrode,the direction of the electric field substantially coincides with the caxis of the bismuth layer structured compound contained in thedielectric layer. Accordingly, since the ferroelectric property of thebismuth layer structured compound can be suppressed and the paraelectricproperty thereof can be fully exhibited, it is possible to fabricate athin film capacitor having a small size and large capacitance.

Further, since the dielectric layer of the dielectric materialcontaining the bismuth layer structured compound whose c axisorientation is improved has a high insulating property, it is possibleto form the dielectric layer thinner and therefore make a thin filmcapacitor much smaller.

Furthermore, since the dielectric layer of the dielectric materialcontaining the bismuth layer structured compound whose c axisorientation is improved has a high insulating property, it is possibleto cause an inorganic EL device to emit light in a desired manner andfabricate an inorganic EL device capable of emitting light having highluminescence by disposing the inorganic EL device on the dielectriclayer of the multi-layered unit according to the present invention,disposing another electrode on the inorganic EL device and applying avoltage between the electrode layer and another electrode.

In the present invention, the dielectric material containing the bismuthlayer structured compound may contain unavoidable impurities.

In a preferred aspect of the present invention, the bismuth layerstructured compound contained in the buffer layer and the bismuth layerstructured compound contained in the dielectric layer have differentcompositions from each other, thereby forming an interface between thebuffer layer and the dielectric layer.

In another preferred aspect of the present invention, the buffer layerand the dielectric layer are formed using different thin film formingprocesses, thereby forming an interface between the buffer layer and thedielectric layer. In this case, the bismuth layer structured compoundcontained in the buffer layer and the bismuth layer structured compoundcontained in the dielectric layer may have the same composition as eachother.

In the present invention, the material for forming the support substrateis not particularly limited insofar as it has conductivity andmechanical strength as a support substrate. Illustrative examples of amaterial for the support substrate include a metal such as platinum(Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold(Au), silver (Ag), copper (Cu), nickel (Ni) or the like, an alloycontaining at least one of these metal as a principal component, aconductive oxide such as NdO, NbO, RhO₂, OsO₂, IrO₂, RuO₂, SrMoO₃,SrRuO₃, CaRuO₃, SrVO₃, SrCrO₃, SrCoO₃, LaNiO₃, Nb doped SrTiO₃ or thelike, a mixture of these, or a conductive glass such as ITO.

In the present invention, the multi-layered unit includes a buffer layerformed on the support substrate and containing a bismuth layerstructured compound oriented in the [001] direction, namely, the c axisdirection. The buffer layer serves to ensure that a dielectric materialcontaining a bismuth layer structured compound having an excellentcharacteristic as a capacitor material can be epitaxially grown thereonto form a dielectric layer of the dielectric material containing thebismuth layer structured compound oriented in the [001], direction,namely, the c axis direction.

Therefore, as the bismuth layer structured compound having an excellentorientation characteristic used to form the buffer layer is selected abismuth layer structured compound different from the bismuth layerstructured compound for forming the dielectric layer.

The bismuth layer structured compound has a composition represented bythe stoichiometric compositional formula: (Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))² or Bi₂A_(m−1)B_(m)O_(3m+3), where the symbol mis a natural number, the symbol A is at least one element selected froma group consisting of sodium (Na), potassium (K), lead (Pb), barium(Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B isat least one element selected from a group consisting of iron (Fe),cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb),tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten(W). In the case where the symbol A and/or B includes two or moreelements, the ratio of the elements can be arbitrarily determined.

As shown in FIG. 1, the bismuth layer structured compound has a layeredstructure formed by alternately laminating perovskite layers 1 eachincluding perovskite lattices 1 a made of (m−1) ABO₃ and (Bi₂O₂)²⁺layers 2.

The number of laminates each consisting of the perovskite layer 1 andthe (Bi₂O₂)²⁺ layer 2 is not particularly limited and it is sufficientfor the bismuth layer structured compound to include at least one pairof (Bi₂O₂)²+ layers 2 and one perovskite layer 1 sandwichedtherebetween.

The c axis of the bismuth layer structured compound means the directionobtained by connecting the pair of (Bi₂O₂) ²⁺ layers 2, namely, the[001] direction.

Among the bismuth layer structured compounds represented by the abovestoichiometric compositional formula, a bismuth layer structuredcompound having an excellent orientation characteristic is used forforming the buffer layer and in the case where a bismuth layerstructured compound where the symbol m is equal to 4 in the generalstoichiometric compositional formula thereof, namely, that representedby the stoichiometric compositional formula: (Bi₂O₂)²⁺ (A₃B₄O₁₃)²⁻ orBi₂A₃ B₄O₁₅, is used as a bismuth layer structured compound for formingthe dielectric layer, a bismuth layer structured compound where thesymbol m is equal to 3 in the general stoichiometric compositionalformula thereof, namely, that represented by the stoichiometriccompositional formula: (Bi₂O₂)²⁺ (A₂B₃O₁₀)²⁻ or Bi₂A₂B₃O₁₂, ispreferably used for forming the buffer layer.

In the present invention, it is not absolutely necessary for the degreeF of orientation in the [001] direction, namely, c axis orientation of abismuth layer structured compound contained in a buffer layer to be 100%but it is sufficient for the degree F of c axis orientation of thebismuth layer structured compound to be equal to or more than 80%. It ismore preferable for the degree of c axis orientation of the bismuthlayer structured compound to be equal to or more than 90% and it is muchmore preferable for the degree of c axis orientation of the bismuthlayer structured compound to be equal to or more than 95%.

The degree F of the c axis orientation of the bismuth layer structuredcompound is defined by the following formula (1).F=(P−P ₀)/(1−P ₀)×100  (1)

In formula (1), P₀ is defined as the X-ray diffraction intensity ofpolycrystal whose orientation is completely random in the c axisdirection, namely, the ratio of the sum ΣI₀ (001) of reflectionintensities I_(o) (001) from the surface of [001] of polycrystal whoseorientation is completely random to the sum ΣI₀ (hkI) of reflectionintensities I₀ (hkI) from the respective crystal surfaces of [hkI]thereof (ΣI₀(001)/ΣI₀ (hkI), and P is defined as X-ray diffractionintensity of the bismuth layer structured compound in the c axisdirection, namely, the ratio of the sum ΣI (001) of reflectionintensities I (001) from the surface of [001] of the bismuth layerstructured compound to the sum ΣI(hkI) of reflection intensities I(hkI)from the respective crystal surfaces of [hkI] thereof (ΣI(001)/ΣI(hkI).The symbols h, k and I can each assume an arbitrary integer value equalto or larger than 0.

In the above formula (1), since P₀ is a known constant, when the sum ΣI(001) of reflection intensities I(001) from the surface of [001] of thebismuth layer structured compound and the sum ΣI(hkI) of reflectionintensities I(hkI) from the respective crystal surfaces of [hkI] areequal to each other, the degree F of the c axis orientation of thebismuth layer structured compound is equal to 100%.

In the present invention, the buffer layer can be formed using any ofvarious thin film forming processes such as a vacuum deposition process,a sputtering process, a pulsed laser deposition process (PLD), a metalorganic chemical vapor deposition process (MOCVD), a chemical solutiondeposition process (CSD process) such as a metal-organic decompositionprocess (MOD) and a sol-gel process or the like. Particularly, in thecase where the buffer layer has to be formed at a low temperature, aplasma CVD process, a photo-CVD process, a laser CVD process, aphoto-CSD process, a laser CSD process or the like is preferably usedfor forming the buffer layer.

In the present invention, the multi-layered unit includes a dielectriclayer made of a dielectric material containing a bismuth layerstructured compound oriented in the [001] direction, namely, the c axisdirection, that is formed on the buffer layer by epitaxially growing adielectric material containing a bismuth layer structured compound:thereon.

In the present invention, the dielectric layer is formed by epitaxiallygrowing a dielectric material containing a bismuth layer structuredcompound on the buffer layer.

Since the dielectric layer is formed by epitaxially growing a dielectricmaterial containing a bismuth layer structured compound; formed on thebuffer layer, it is possible to reliably orient the bismuth layerstructured compound contained in the dielectric layer in the [001],direction, namely, the c axis direction. Therefore, in the case where athin film capacitor is fabricated using the multi-layered unit accordingto the present invention, since the bismuth layer structured compounddoes not function as a ferroelectric material but functions as aparaelectric material, it is possible to fabricate a thin film capacitorhaving a small size, large capacitance and an excellent dielectriccharacteristic using the multi-layered unit according to the presentinvention.

In the present invention, it is not absolutely necessary for the degreeF of orientation in the [001] direction, namely, c axis orientation ofthe bismuth layer structured compound contained in the dielectric layerto be 100% and it is sufficient for the degree F of c axis orientationto be equal to or more than 80%. It is more preferable for the degree ofc axis orientation of the bismuth layer structured compound to be equalto or more than 90% and it is much more preferable for the degree of caxis orientation of the bismuth layer structured compound to be equal toor more than 95%.

The dielectric characteristic of a dielectric layer can be markedlyimproved by orienting the bismuth layer structured compound in the [001]direction, namely, the c axis direction in this manner.

More specifically, in the case where a thin film capacitor is fabricatedby forming, for example, an upper electrode on the dielectric layer ofthe multi-layered unit according to the present invention, even if thethickness of the dielectric layer is equal to or thinner than, forexample, 100 nm, a thin film capacitor having a relatively highdielectric constant and low loss (tan δ) can be obtained. Further, athin film capacitor having an excellent leak characteristic, an improvedbreakdown voltage, an excellent temperature coefficient of thedielectric constant and an excellent surface smoothness can be obtained.

In the present invention, from among the above mentioned bismuth layerstructured compounds, a bismuth layer structured compound having anexcellent characteristic as a capacitor material and different from thatcontained in the buffer layer is selected as the bismuth layerstructured compound for forming the dielectric layer.

When a bismuth layer structured compound where the symbol m is equal to3 in the general stoichiometric compositional formula of a bismuth layerstructured compound, namely, that represented by the stoichiometriccompositional formula: (Bi₂O₂)²⁺ (A₂B₃O₁₀)²⁻ or Bi₂A₂ B₃O₁₂, is used forforming the buffer layer, a bismuth layer structured compound where thesymbol m is equal to 4 in the general stoichiometric compositionalformula of a bismuth layer structured compound, namely, that representedby the stoichiometric compositional formula: (Bi₂O₂)²⁺ (A₃B₄O₁₃)²⁻ orBi₂A₃ B₄O₁₅, is preferably used as a bismuth layer structured compoundfor forming the dielectric layer.

In the present invention, it is particularly preferable that the bismuthlayer structured compound contained in the dielectric layer has acomposition represented by the stoichiometric compositional formula:Ca_(x)Sr_((1-x))Bi₄Ti₄O₁₅, where x is equal to or larger than 0 andequal to or smaller than 1. If the bismuth layer structured compoundhaving such a composition is used, a dielectric layer having arelatively large dielectric constant can be obtained and the temperaturecharacteristic thereof can be further improved.

In the present invention, parts of the elements represented by thesymbols A or B in the stoichiometric compositional formula of thebismuth layer structured compound contained in the dielectric layer arepreferably replaced with at least one element Re (yttrium (Y) or arare-earth element) selected from the group consisting of scandium (Sc),yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium(Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd),terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm)ytterbium (Yb) and lutetium (Lu).

The preferable amount of replacement by the element Be depends upon thevalue of the symbol m. For example, in the case where the symbol m isequal to 3, in the compositional formula: Bi₂A_((2-x))Re_(x)B₃O₁₂, x ispreferably equal to or larger than 0.4 and equal to or smaller than 1.8and more preferably equal to or larger than 1.0 and equal to or smallerthan 1.4. If the amount of replacement by the element Re is determinedwithin this range, the Curie temperature (phase transition temperaturefrom ferroelectric to paraelectric) of the dielectric layer can becontrolled preferably to be equal to or higher than −100° C. and equalto or lower than 100° C. and more preferably to be equal to or higherthan −50° C. and equal to or lower than 50° C. If the Curie point isequal to or higher than −100° C. and equal to or lower than 100° C., thedielectric constant of the dielectric thin film 6 increases. The Curietemperature can be measured by DSC (differential scanning calorimetry)or the like. If the Curie point becomes lower than room temperature (25°C.), tan δ further decreases and, as a result, the loss value Q furtherincreases.

Furthermore, in the case where the symbol m is equal to 4 in the generalstoichiometric compositional formula of a bismuth layer structuredcompound, in the compositional formula: Bi₂A_((3-x))Re_(x)B₄O₁₅, x ispreferably equal to or larger than 0.01 and equal to or smaller than 2.0and more preferably equal to or larger than 0.1 and equal to or smallerthan 1.0.

Although the dielectric layer of the multi-layered unit according to thepresent invention has an excellent leak characteristic even if it doesnot contain the element Re, it is possible to further improve the leakcharacteristic by replacing part of the elements represented by thesymbols A or B with the element Re.

For example, even in the case where no part of the elements representedby the symbols A or B in the stoichiometric compositional formula of thebismuth layer structured compound is replaced with element Re, the leakcurrent measured at the electric filed strength of 50 kV/cm can becontrolled preferably to be equal to or lower than 1×10⁻⁷ A/cm² and morepreferably to be equal to or lower than 5×10⁻⁸ A/cm² and the shortcircuit ratio can be controlled preferably to be equal to or lower than10% and more preferably to be equal to or lower than 5%. However, in thecase where parts of the elements represented by the symbols A or B inthe stoichiometric compositional formula of the bismuth layer structuredcompound are replaced with element Re, the leak current measured underthe same condition can be controlled preferably to be equal to or lowerthan 5×10⁻⁸ A/cm² and more preferably to be equal to or lower than1×10⁻⁸ A/cm² and the short circuit ratio can be controlled preferably tobe equal to or lower than 5% and more preferably to be equal to or lowerthan 3%.

In the present invention, the dielectric layer can be formed using anyof various thin film forming processes such as a vacuum depositionprocess, a sputtering process, a pulsed laser deposition process (PLD),a metal organic chemical vapor deposition process (MOCVD), a chemicalsolution deposition process (CSD process) such as a metal-organicdecomposition process (MOD) and a sol-gel process or the like.Particularly, in the case where the dielectric layer has to be formed ata low temperature, a plasma CVD process, a photo-CVD process, a laserCVD process, a photo-CSD process, a laser CSD process or the like ispreferably used for forming the dielectric layer.

In the case of forming a dielectric layer using a metal-organicdecomposition process, a spin coating process is often utilized.However, in the present invention, in the case where the supportsubstrate is formed of a flexible material such as a metal, alloy or thelike, it is also possible to form a dielectric layer on the buffer layerusing a simpler coating process such as a dip coating process and thencalcining?baking? the dielectric layer to epitaxially grow the bismuthlayer structured compound contained in the dielectric material. Thismakes it possible to form the dielectric layer and fabricate themulti-layered unit with high efficiency.

The above and other objects and features of the present invention willbecome apparent from the following description made with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing schematically showing the structure of a bismuthlayer structured compound.

FIG. 2 is a schematic partial cross-sectional view showing amulti-layered unit which is a preferred embodiment of the presentinvention.

FIG. 3 is a schematic partial cross-sectional view showing a thin filmcapacitor fabricated using a multi-layered unit which is a preferredembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a schematic partial cross-sectional view showing amulti-layered unit which is a preferred embodiment of the presentinvention.

As shown in FIG. 2, a multi-layered unit 1 according to this embodimentis constituted by laminating a buffer layer 3 and a dielectric layer 4on a support substrate 2 in this order.

In this embodiment, the support substrate 2 of the multi-layered unit 1is formed of platinum (Pt).

Therefore, the support substrate 2 serves to mechanically support themulti-layered unit 1 and also serves as an electrode layer of themulti-layered unit 1.

The thickness of the support substrate 2 is determined so that itsmechanical strength is sufficient for mechanically supporting themulti-layered unit 1.

As shown in FIG. 2, the multi-layered unit 1 according to thisembodiment includes a buffer layer 3 of a dielectric material containinga bismuth layer structured compound on the support substrate 2.

In this embodiment, a bismuth layer structured compound having anexcellent orientation characteristic and having a compositionrepresented by the stoichiometric compositional formula: Bi₄Ti₃O₁₂ wherethe symbol m is equal to 3 and the symbol A is replaced by Bi in thegeneral stoichiometric compositional formula thereof is selected as abismuth layer structured compound for forming a buffer layer 3 and thebismuth layer structured compound contained in the buffer layer 3 isoriented in the [001] direction, namely, the c axis direction.

In this embodiment, the buffer layer 3 of the dielectric materialcontaining a bismuth layer structured compound having a compositionrepresented by Bi₄Ti₃O₁₂ is formed by a metal organic chemical vapordeposition process (MOCVD), for example.

In the case where a buffer layer 3 of the dielectric material containinga bismuth layer structured compound having a composition represented byBi₄Ti₃O₁₂ is formed by a metal organic chemical vapor deposition process(MOCVD), for example, Bi(CH₃)₃ and Ti(O-i-C₃H₇)₄ are used as constituentgases and the temperature of the the support substrate 2 of platinum(Pt) is maintained at 550° C., thereby forming a buffer layer 3 having athickness of 50 nm and oriented in the [001] direction, namely, the caxis direction.

In this embodiment, the buffer layer 3 serves to ensure that adielectric layer 4 of a dielectric material containing a bismuth layerstructured compound oriented in the [001] direction, namely, the c axisdirection, can be formed by epitaxially growing a dielectric materialcontaining a bismuth layer structured compound thereon.

As shown in FIG. 2, the multi-layered unit 1 according to thisembodiment includes a dielectric layer 4 formed-on the buffer layer 3.

In this embodiment, the dielectric layer 4 is formed of a dielectricmaterial containing a bismuth layer structured compound having acomposition represented by the stoichiometric compositional formula:SrBi₄Ti₄O₁₅ where the symbol m is equal to 4 and the symbol A₃ isreplaced by Bi₂+Sr in the general stoichiometric compositional formulathereof and having an excellent characteristic as a capacitorcharacteristic.

In this embodiment, the dielectric layer 4 is formed on the buffer layer3 using a metal organic deposition (MOD) process.

Concretely, a toluene solution of 2-ethyl hexanoate Sr, a 2-ethylhexanoate solution of 2-ethyl hexanoate Bi and a toluene solution of2-ethyl hexanoate Ti are stoichiometrically mixed so that the mixturecontains 1 mole of 2-ethyl hexanoate Sr, 4 moles of 2-ethyl hexanoate Biand 4 moles of 2-ethyl hexanoate Ti and is diluted with toluene. Theresultant constituent solution is coated on the buffer layer 3 using aspin coating method and after drying the resultant dielectric layer 4 istentatively baked at a temperature under which the dielectric layer 4cannot be crystallized.

The same constituent solution is coated on the thus tentatively bakeddielectric layer 4 using a spin coating method to form a coating layerand the coating layer is dried and tentatively baked. These operationsare repeated.

When tentative baking is completed, the dielectric layer 4 is baked anda series of operations including coating, drying, tentative baking,coating, drying, tentative baking and baking are repeated until adielectric layer 4 having a required thickness, for example, 100 nm isobtained.

During these processes, a dielectric material containing a bismuth layerstructured compound is epitaxially grown and a dielectric layer 4oriented in the [001] direction, namely, the c axis direction is formed.

According to this embodiment, since the support substrate 2 of themulti-layered unit 1 is formed of a conductive material, the supportsubstrate 2 can serve as an electrode layer and it is therefore possibleto make a thin film capacitor fabricated using the multi-layered unit 1according to this embodiment much thinner.

Further, according to this embodiment, the dielectric layer 4 of themulti-layered unit 1 is formed by epitaxially growing a dielectricmaterial containing a bismuth layer structured compound represented bythe stoichiometric compositional formula: SrBi₄Ti₄O₁₅ and having anexcellent characteristic as a capacitor material on the buffer layer 3formed of a bismuth layer structured compound represented by thestoichiometric compositional formula: Bi₄Ti₃O₁₂, having an excellentorientation characteristic and oriented in the [001] direction, namely,the c axis direction. Therefore, it is possible to reliably orient thebismuth layer structured compound contained in the dielectric layer 4 inthe [001] direction, namely, the c axis direction.

Therefore, according to this embodiment, since the multi-layered unit 1includes the dielectric layer 4 formed of the dielectric materialcontaining the bismuth layer structured compound oriented in the [001]direction, namely, the c axis direction, in the case of, for example,providing an upper electrode on the dielectric layer 4 of themulti-layered unit 1 according to this embodiment to fabricate a thinlayer capacitor and applying a voltage between the support substrate 2serving as an electrode layer and the upper electrode, the direction ofthe electric field substantially coincides with the c axis of thebismuth layer structured compound contained in the dielectric layer 4.Accordingly, since the ferroelectric property of the bismuth layerstructured compound can be suppressed and the paraelectric propertythereof can be fully exhibited, it is possible to fabricate a thin filmcapacitor having a small size and large capacitance.

Further, according to this embodiment, since the multi-layered unit 1includes a dielectric layer 4 formed of a dielectric material containinga bismuth layer structured compound oriented in the [001] direction,namely, the c axis direction, and the dielectric layer 4 containing thebismuth layer structured compound whose c axis orientation is improvedhas a high insulating property, the dielectric layer 6 can be madethinner. Therefore, it is possible to make a thin film capacitor muchthinner.

Furthermore, according to this embodiment, the buffer layer 3 having athickness of 10 nm is formed using a metal organic chemical vapordeposition (MOCVD) process so as to enable epitaxial growth of a bismuthlayer structured compound having an excellent capacitor characteristicthereon and form a dielectric layer 4 containing the bismuth layerstructured compound reliably oriented in the [001] direction, namely,the c axis direction and, on the other hand, the dielectric layer 4 onwhich no layer is formed using an epitaxial growth process and which hasa thickness larger than that of the buffer layer 3 is formed using ametal organic decomposition (MOD) process, which is an inexpensiveprocess. Therefore, it is possible to decrease the cost of fabricating amulti-layered unit 1.

FIG. 3 is a schematic partial cross-sectional view showing a thin filmcapacitor fabricated using a multi-layered unit which is a preferredembodiment of the present invention.

As shown in FIG. 3, the thin film capacitor 10 includes themulti-layered unit 1 shown in FIG. 2 and an upper electrode 11 formed onthe dielectric layer 4 of the multi-layered unit 1.

In this embodiment, the support substrate 2 of the multi-layered unit 1serves to ensure the mechanical strength of the entire thin filmcapacitor 10 and also serves as one of electrodes of the thin filmcapacitor 10.

In this embodiment, the dielectric layer 4 of the multi-layered unit 1serves as a dielectric layer of the thin film capacitor 10.

In this embodiment, the upper electrode 11 serving as the other of theelectrodes of the thin film capacitor 10 is formed on the dielectriclayer 4 of the multi-layered unit 1.

The material for forming the upper electrode is not particularly limitedinsofar as it has conductivity and the upper electrode 11 can be formedof a metal such as platinum (Pt), ruthenium (Ru), rhodium (Rh),palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu),nickel (Ni) or the like, an alloy containing at least one of these metalas a principal component, a conductive oxide such as NdO, NbO, RhO₂,OsO₂, IrO₂, RuO₂, SrMo₃, SrRuO₃, CaRuO₃, SrVO₃, SrCrO₃, SrCoO₃, LaNiO₃,Nb doped SrTiO₃ or the like, or a mixture of these and a conductiveglass such as ITO. Further, unlike the support substrate 2 of themulti-layered unit 1 serving as an electrode layer, since it isunnecessary to consider the lattice mismatch with the material forforming the dielectric layer 4 when a material for forming the upperelectrode 11 is to be selected and it can be formed at room temperature,the upper electrode 11 can be formed using a base metal such as iron(Fe), cobalt (Co) or the like or an alloy such as WSi, MoSi or the like.The thickness of the upper electrode 11 is not particularly limitedinsofar as it can serve as the other of the electrodes of the thin filmcapacitor 10 and the upper electrode 11 can be formed so as to have athickness of 10 to 10,000 nm, for example.

The method for forming the upper electrode 11 is not particularlylimited and the upper electrode 11 can be formed using any of variousthin film forming processes such as a vacuum deposition process, asputtering process, a pulsed laser deposition process (PLD), a metalorganic chemical vapor deposition process (MOCVD), a chemical solutiondeposition process (CSD process) such as a metal-organic decompositionprocess (MOD) and a sol-gel process or the like. Among these, asputtering process is preferable from the viewpoint of formation speed.

In the thus constituted thin layer capacitor 10, the bismuth layerstructured compound contained in the dielectric layer 4 is oriented sothat the c axis thereof is substantially perpendicular to the supportsubstrate 2 serving as an electrode layer and the upper electrode 11.Therefore, when a voltage is applied between the support substrate 2serving as an electrode layer and the upper electrode 11, the directionof the electric field substantially coincides with the c axis of thebismuth layer structured compound contained in the dielectric layer 4.As a result, since the ferroelectric property of the bismuth layerstructured compound contained in the dielectric layer 4 can besuppressed and the paraelectric property thereof can be fully exhibited,it is possible to fabricate a thin film capacitor having a small sizeand large capacitance.

A thin film capacitor having such characteristics can be preferablyutilized as a decoupling capacitor, in particular, a decouplingcapacitor for an LSI having a high operating frequency.

The present invention has thus been shown and described with referenceto specific embodiments. However, it should be noted that the presentinvention is in no way limited to the details of the describedarrangements but changes and modifications may be made without departingfrom the scope of the appended claims.

For example, in the above described embodiments, although the supportsubstrate 2 of the multi-layered unit 1 is formed of platinum (Pt), itis not absolutely necessary to form the support substrate 2 of platinum(Pt) and the material for forming the support substrate 2 is notparticularly limited insofar as it has conductivity and mechanicalstrength as a support substrate. The support substrate 2 may, forexample, be formed not of platinum (Pt) but of a metal such as ruthenium(Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver(Ag), copper (Cu), nickel (Ni) or the like, an alloy containing at leastone of these metal as a principal component, a conductive oxide such asNdO, NbO, RhO₂, OsO₂, IrO₂, RuO₂, SrMoO₃, SrRuO₃, CaRuO₃, SrVO₃, SrCrO₃,SrCoO₃, LaNiO₃, Nb doped SrTiO₃ or the like, or a mixture of these.

Further, in the above described embodiments, the multi-layered unit 1includes the buffer layer 3 formed on the support substrate 2 and formedof the bismuth layer structured compound having an excellent orientationcharacteristic and having a composition represented by thestoichiometric compositional formula: Bi₄Ti₃O₁₂ where the symbol m isequal to 3 and the symbol A is replaced by Bi in the generalstoichiometric compositional formula thereof. However, it is notabsolutely necessary to form the buffer layer 3 of the bismuth layerstructured compound having a composition represented by thestoichiometric compositional formula: Bi₄Ti₃O₁₂ where the symbol m isequal to 3 and the symbol A is replaced by Bi in the generalstoichiometric compositional formula thereof and the buffer layer 3 maybe formed of a dielectric material containing a bismuth layer structuredcompound where the symbol m is not equal to 3 or a dielectric materialcontaining another bismuth layer structured compound whose constituentelements are different from Bi₄Ti₃O₁₂ insofar as it has an excellentorientation characteristic.

Furthermore, in the above described embodiments, although the bufferlayer 3 is formed using a metal organic chemical vapor depositionprocess (MOCVD), it is not absolutely necessary to form the buffer layer3 using a metal-organic chemical vapor deposition process and the bufferlayer 3 may be formed using other thin film forming process such as avacuum deposition process, a sputtering process, a pulsed laserdeposition process (PLD), a chemical solution deposition process (CSDprocess) such as a metal-organic decomposition process (MOD) and asol-gel process or the like. In the case where the support substrate 2is formed of a flexible material such as metal, alloy or the like, it isalso possible to form a buffer layer 4 using a coating process such as adip coating process.

Moreover, in the above described embodiments, the multi-layered unit 1includes the dielectric layer 4 formed on the buffer layer 3 of adielectric material containing a bismuth layer structured compoundhaving a composition represented by the stoichiometric compositionalformula: SrBi₄Ti₄O₁₅ where the symbol m is equal to 4 and the symbol A₃is replaced by Bi₂+Sr in the general stoichiometric compositionalformula thereof. However, it is not absolutely necessary to form on thebuffer layer 3 a dielectric layer 4 of a dielectric material containinga bismuth layer structured compound having a composition represented bythe stoichiometric compositional formula: SrBi₄Ti₄O₁₅ where the symbol mis equal to 4 and the symbol A₃ is replaced by Bi₂+Sr in the generalstoichiometric compositional formula thereof and the dielectric layer 4may be formed of a dielectric material containing a bismuth layerstructured compound where the symbol m is not equal to 4 or a dielectricmaterial containing another bismuth layer structured compound whoseconstituent elements are different from SrBi₄Ti₄O₁₅ insofar as it has anexcellent characteristic as a capacitor material.

Further, in the above described embodiments, although the dielectriclayer 4 of the multi-layered unit 1 is formed using a metal-organicdecomposition process (MOD), it is not absolutely necessary to form thedielectric layer 4 using a metal-organic decomposition process and thedielectric layer 4 may be formed using some other thin film formingprocess such as a vacuum deposition process, a sputtering process, apulsed laser deposition process (PLD), a metal organic chemical vapordeposition process (MOCVD), other chemical solution deposition process(CSD process) such as a sol-gel process or the like. In the case wherethe support substrate 2 is formed of a flexible material such as metal,alloy or the like, it is also possible to form the dielectric layer 4 onthe buffer layer using a coating process such as a dip coating processand then baking it, thereby epitaxially growing a bismuth layerstructured compound contained in the dielectric layer 4.

Furthermore, in the above described embodiments, the multi-layered unit1 includes the buffer layer 3 formed on the support substrate 2 andformed of a dielectric material containing a bismuth layer structuredcompound having a composition represented by Bi₄Ti₃O₁₂ wherein thesymbol m is equal to 3 and the symbol A is replaced by Bi in the generalstoichiometric compositional formula thereof and having an excellentorientation characteristic and the dielectric layer 4 formed on thebuffer layer 3 of a dielectric material containing a bismuth layerstructured compound having a composition represented by SrBi₄Ti₄O₁₅where the symbol m is equal to 4 and the symbol A₃ is replaced by Bi₂+Srin the general stoichiometric compositional formula thereof, and thebuffer layer 3 and the dielectric layer 4 are formed of dielectricmaterials containing bismuth layer structured compounds having differentcompositions. However, if an interface is formed between the bufferlayer 3 and the dielectric layer 4, the buffer layer 3 and thedielectric layer 4 may be formed using different thin film formingprocesses so as to contain bismuth layer structured compound having thesame composition.

Moreover, in the above described embodiments, although the multi-layeredunit 1 is used as a component of a thin film capacitor, themulti-layered unit 1 can be used not only as a component of a thin filmcapacitor but also as a multi-layered unit for causing an inorganic EL(electro-luminescence) device to emit light having high luminescence.Specifically, although an insulating layer having a high insulatingproperty is necessary between an electrode layer and an inorganic ELdevice in order to cause the inorganic EL device to emit light havinghigh luminescence, since a dielectric layer 4 of a dielectric materialcontaining a bismuth layer structured compound having an improved c axisorientation has a high insulating property, it is possible to cause aninorganic EL device to emit light in a desired manner by disposing theinorganic EL device on the dielectric layer 4, disposing anotherelectrode on the inorganic EL device and applying a voltage between thesupport substrate serving as an electrode layer and the other electrode.

According to the present invention, it is possible to provide amulti-layered unit suitable for fabricating a thin film capacitor havinga small size and a large capacitance and suitable for fabricating aninorganic EL (electro-luminescence) device capable of emitting lighthaving high luminescense.

1. A multi-layered unit constituted by forming on a support substrateformed of a conductive material, a buffer layer containing a bismuthlayer structured compound oriented in the [001] direction and adielectric layer of a dielectric material containing a bismuth layerstructured compound epitaxially grown and oriented in the [001]direction in this order, a bismuth layer structured compound having anexcellent orientation characteristic being selected as the bismuth layerstructured compound contained in the buffer layer and a bismuth layerstructured compound having an excellent characteristic as a capacitormaterial being selected as the bismuth layer structured compoundcontained in the dielectric layer, thereby forming an interface betweenthe buffer layer and the dielectric layer.
 2. A multi-layered unit inaccordance with claim 1, wherein the bismuth layer structured compoundcontained in the buffer layer and the bismuth layer structured compoundcontained in the dielectric layer have different compositions.
 3. Amulti-layered unit in accordance with claim 2, wherein the supportsubstrate is formed of at least one material selected from a groupconsisting of metals including platinum (Pt), ruthenium (Ru), rhodium(Rh), palladium (Pd), iridium (ar), gold (Au), silver (Ag), copper (Cu)and nickel (Ni), alloys containing at least one of these metals as aprincipal component, conductive oxides having a perovskite structure andincluding NdO, NbO, RhO₂, OsO₂, IrO₂, RuO₂, SrMoO₃, SrRuO₃, CaRuO₃,SrVO₃, SrCrO₃, SrCoO₃, LaNiO₃ or Nb doped SrTiO₃, and mixtures of these.4. A multi-layered unit in accordance with claim 3 wherein the bufferlayer contains a bismuth layer structured compound having a compositionrepresented by a stoichiometric compositional formula: (Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))²⁻ or Bi₂A_(m−1)B_(m)O_(3m+3), where the symbol mis a natural number, the symbol A is at least one element selected froma group consisting of sodium (Na), potassium (K), lead (Pb), barium(Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B isat least one element selected from a group consisting of iron (Fe),cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb),tantalum (Ta), antimony (Sb), vanadium A), molybdenum (Mo) and tungsten(W) and when the symbol A and/or B includes two or more elements, theratio of the elements is arbitrarily determined.
 5. A multi-layered unitin accordance with claim 4, wherein the dielectric layer contains abismuth layer structured compound having a composition represented by astoichiometric compositional formula: (Bi₂O₂)²⁺ (A_(m−1)B_(m)O_(3m+1))²⁻or Bi₂A_(m−1)B_(m)O_(3m+3), where the symbol m is a natural number, thesymbol A is at least one element selected from a group consisting ofsodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr),calcium (Ca) and bismuth (Bi), and the symbol B is at least one elementselected from a group consisting of iron (Fe), cobalt (Co), chromium(Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony(Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbolA and/or B includes two or more elements, the ratio of the elements isarbitrarily determined.
 6. A multi-layered unit in accordance with claim5, wherein the buffer layer contains the bismuth layer structuredcompound wherein the symbol m is equal to 3 and the dielectric layercontains the bismuth layer structured compound wherein the symbol m isequal to
 4. 7. A multi-layered unit in accordance with claim 3, whereinthe dielectric layer contains a bismuth layer structured compound havinga composition represented by a stoichiometric compositional formula:(Bi₂O₂)²⁺ (A_(m−1)B_(m)O_(3m+1))²⁻ or Bi₂A_(m−1)B_(m)O_(3m+3), where thesymbol m is a natural number, the symbol A is at least one elementselected from a group consisting of sodium (Na), potassium (K), lead(Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (ii), andthe symbol B is at least one element selected from a group consisting ofiron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti),niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum(Mo) and tungsten (W) and when the symbol A and/or B includes two ormore elements, the ratio of the elements is arbitrarily determined.
 8. Amulti-layered unit in accordance with claim 7, wherein the buffer layercontains the bismuth layer structured compound wherein the symbol m isequal to 3 and the dielectric layer contains the bismuth layerstructured compound wherein the symbol m is equal to
 4. 9. Amulti-layered unit in accordance with claim 2, wherein the buffer layercontains a bismuth layer structured compound having a compositionrepresented by a stoichiometric compositional formula: (Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))²⁻ or Bi₂A_(m−1)B_(m)O_(3m+3), where the symbol mis a natural number, the symbol A is at least one element selected froma group consisting of sodium (Na), potassium (K), lead (Pb), barium(Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B isat least one element selected from a group consisting of iron (Fe),cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb),tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten(W) and when the symbol A and/or B includes two or more elements, theratio of the elements is arbitrarily determined.
 10. A multi-layeredunit in accordance with claim 9 wherein the dielectric layer contains abismuth layer structured compound having a composition represented by astoichiometric compositional formula: (Bi₂O₂)²⁺ (A_(m−1)B_(m)O_(3m+1))²⁻or Bi₂A_(m−1)B_(m)O_(3m+3), where the symbol m is a natural number, thesymbol A is at least one element selected from a group consisting ofsodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr),calcium (Ca) and bismuth (ii), and the symbol B is at least one elementselected from a group consisting of iron (Fe), cobalt (Co), chromium(Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony(Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbolA and/or B includes two or more elements, the ratio of the elements isarbitrarily determined.
 11. A multi-layered unit in accordance withclaim 10, wherein the buffer layer contains the bismuth layer structuredcompound wherein the symbol m is equal to 3 and the dielectric layercontains the bismuth layer structured compound wherein the symbol m isequal to
 4. 12. A multi-layered unit in accordance with claim 2, whereinthe dielectric layer contains a bismuth layer structured compound havinga composition represented by a stoichiometric compositional formula:(Bi₂O₂)²⁺ (A_(m−1)B_(m)O_(3m+1))²⁻ or Bi₂A_(m−1)B_(m)O_(3m+3), where thesymbol m is a natural number, the symbol A is at least one elementselected from a group consisting of sodium (Na), potassium (K), lead(Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), andthe symbol B is at least one element selected from a group consisting ofiron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti),niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum(Mo) and tungsten (W) and when the symbol A and/or B includes two ormore elements, the ratio of the elements is arbitrarily determined. 13.A multi-layered unit in accordance with claim 12, wherein the bufferlayer contains the bismuth layer structured compound wherein the symbolm is equal to 3 and the dielectric layer contains the bismuth layerstructured compound wherein the symbol m is equal to
 4. 14. Amulti-layered unit in accordance with claim 1, wherein the supportsubstrate is formed of at least one material selected from a groupconsisting of metals including platinum (Pt), ruthenium (Ru), rhodium(Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu)and nickel (Ni), alloys containing at least one of these metals as aprincipal component, conductive oxides having a perovskite structure andincluding NdO, NbO, RhO₂, OSO₂, IrO₂, RuO₂, SrMoO₃, SrRuO₃, CaRuO₃,SrVO₃, SrCrO₃, SrCoO₃, LaNiO₃ or Nb doped SrTiO₃, and mixtures of these.15. A multi-layered unit in accordance with claim 14, wherein the bufferlayer contains a bismuth layer structured compound having a compositionrepresented by a stoichiometric compositional formula: (Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))²⁻ or Bi₂A_(m−1)B_(m)O_(3m+3), where the symbol mis a natural number, the symbol A is at least one element selected froma group consisting of sodium (Na), potassium (K), lead (Pb), barium(Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B isat least one element selected from a group consisting of iron (Fe),cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ai), niobium (Nb),tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten(W) and when the symbol A and/or B includes two or more element, theratio of the elements is arbitrarily determined.
 16. A multi-layeredunit in accordance with claim 15, wherein the dielectric layer containsa bismuth layer structured compound having a composition represented bya stoichiometric compositional formula: (Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))²⁻ or Bi₂A_(m−1)B_(m)O_(3m+3), where the symbol mis a natural number, the symbol A is at least one element selected froma group consisting of sodium (Na), potassium (K), lead (Pb), barium(Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B isat least one element selected from a group consisting of iron (Fe),cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb),tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten(W) and when the symbol A and/or B includes two or more elements, theratio of the elements is arbitrarily determined.
 17. A multi-layeredunit in accordance with claim 16, wherein the buffer layer contains thebismuth layer structured compound wherein the symbol m is equal to 3 andthe dielectric layer contains the bismuth layer structured compoundwherein the symbol m is equal to
 4. 18. A multi-layered unit inaccordance with claim 14 wherein the dielectric layer contains a bismuthlayer structured compound having a composition represented by astoichiometric compositional formula: (Bi₂O₂)²⁺ (A_(m−1)B_(m)O_(3m+1))²⁻or Bi₂A_(m−1)B_(m)O_(3m+3), where the symbol m is a natural number, thesymbol A is at least one element selected from a group consisting ofsodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr),calcium (Ca) and bismuth (Bi), and the symbol B is at least one elementselected from a group consisting of iron (Fe), cobalt (Co), chromium(Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony(Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbolA and/or B includes two or more elements, the ratio of the elements isarbitrarily determined.
 19. A multi-layered unit in accordance withclaim 18, wherein the buffer layer contains the bismuth layer structuredcompound wherein the symbol m is equal to 3 and the dielectric layercontains the bismuth layer structured compound wherein the symbol m isequal to
 4. 20. A multi-layered unit in accordance with claim 1, whereinthe buffer layer contains a bismuth layer structured compound having acomposition represented by a stoichiometric compositional formula:(Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))²⁻ or Bi₂A_(m−1)B_(m)O_(3m+3), where thesymbol m is a natural number, the symbol A is at least one elementselected from a group consisting of sodium (Na), potassium (K), lead(Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), andthe symbol B is at least one element selected from a group consisting ofiron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti),niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum(Mo) and tungsten (W) and when the symbol A and/or B includes two ormore elements, the ratio of the elements is arbitrarily determined. 21.A multi-layered unit in accordance with claim 20, wherein the dielectriclayer contains a bismuth layer structured compound having a compositionrepresented by a stoichiometric compositional formula: (Bi₂O₂)²⁺(A_(m−1)B_(m)O_(3m+1))²⁻ or Bi₂A_(m−1)B_(m)O_(3m+3), where the symbol mis a natural number, the symbol A is at least one element selected froma group consisting of sodium (Na), potassium (K), lead (Pb), barium(Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B isat least one element selected from a group consisting of iron (Fe),cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb),tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten(W) and when the symbol A and/or B includes two or more elements, theratio of the elements is arbitrarily determined.
 22. A multi-layeredunit in accordance with claim 21, wherein the buffer layer contains thebismuth layer structured compound wherein the symbol m is equal to 3 andthe dielectric layer contains the bismuth layer structured compoundwherein the symbol m is equal to
 4. 23. A multi-layered unit inaccordance with claim 1, wherein the dielectric layer contains a bismuthlayer structured compound having a composition represented by astoichiometric compositional formula: (Bi₂O₂)²⁺ (A_(m−1)B_(m)O_(3m+1))²⁻or Bi₂A_(m−1)B_(m)O_(3m+3), where the symbol m is a natural number, thesymbol A is at least one element selected from a group consisting ofsodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr),calcium (Ca) and bismuth (Bi), and the symbol B is at least one elementselected from a group consisting of iron (Fe), cobalt (Co), chromium(Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony(Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbolA and/or B includes two or more elements, the ratio of the elements isarbitrarily determined.
 24. A multi-layered unit in accordance withclaim 23, wherein the buffer layer contains the bismuth layer structuredcompound wherein the symbol m is equal to 3 and the dielectric layercontains the bismuth layer structured compound wherein the symbol m isequal to 4.